It is common practice to employ partially reflective--partially transmissive metal layer bearing films in glazing structures. These films may be applied to the surface of glass window glazing materials. They may be laminated into glazing structures. They may be suspended alone or in combination with other sheets of glazing. These products typically have a plastic film substrate which carries the reflector metal layer adherent to it. As will be described in more detail, plastic films are often marketed with a coating, known in the art as a slip coating, on one side to facilitate handling during production and fabrication. The side of the film having the slip coating is called (not unexpectedly) the "slip" side. The other side is the "nonslip" side.
These reflector products, as a general class may be prepared by applying the reflective layer to the film with a wide range of chemical mirroring methods, vapor deposition processes and sputter deposition techniques. In sputtering, a plasma is created between two electrodes in a high vacuum chamber. This plasma causes atoms of one electrode (the target) which is either metal or a metal compound, to be dislodged and drawn toward the other electrode. The plastic film substrate is placed between the electrodes and the material dislodged from the target is deposited upon the substrate.
Sputtering processes are often accompanied by a pretreatment step called preglow. Preglow also employs a plasma that is generated under conditions such that little or no material is deposited upon the substrate.
One simple format for these films used heretofore involves a single partially transparent metal reflector layer adherent to one side of the plastic film. Another widely employed format has a partially transparent, partially reflective sequence of dielectric and metal layers on one side of the film.
Also in the past it has been proposed to place reflective layers on both sides of a plastic film. This has not found acceptance typically because the plastic substrate tends to degrade or discolor prematurely when this is done. This has been a vexing problem since double-sided materials do possess certain theoretical performance advantages.